Arkansas weed control: Avoid glyphosate drift to rice late

Bob Scott | May 27, 2005

This time of year most of you are working hard and under lots of pressure to get all the work done. Hopefully the wind is cooperating more with you this year than it has the last couple of years. We are due an easy spring in terms of spraying and avoiding drift. We probably won't get it, but we can always hope.

Before the advent of so many Roundup Ready crops and cheap glyphosate for burn-down, I never gave much thought to how sensitive rice was to glyphosate drift. Now it can be all too evident. Extreme caution is needed when spraying glyphosate next to rice.

Glyphosate drift on young rice can cause severe injury or death, depending on the rate of drift. Unlike corn, which is very sensitive to glyphosate, rice is a bit more tolerant to glyphosate drift in terms of its ability to grow out of the injury.

Usually lower rates of glyphosate drift early to rice will result in a 10 to 20 percent loss of yield, but the seedheads and flag leaves will appear normal when they emerge.

I have at times (though seldom) had to recommend replanting rice because of early glyphosate drift. Later in the spring, yield potential of late-planted rice often is no better than letting the rice that is sick grow out of it.

Symptoms of glyphosate drift resemble high salt or pH damage. They include stunting, chlorosis and some necrotic/dead leaves. Basically little yellow sick rice is little yellow sick rice, and it can be hard to tell some symptoms from others.

Symptoms of Newpath drift from a Clearfield rice field can look very similar to the ailments listed above. Newpath damage in terms of yield loss may be worse than glyphosate on small rice early in the season.

Later in the season, be very cautious spraying Roundup Ready soybeans or other Roundup Ready crops around rice that has reached the panicle initiation stage (also called green ring or PI). Glyphosate drift to rice at this stage may be difficult to see. Around 14 days after treatment, a small black necrotic area may be visible around the developing seedhead. This can be seen by splitting open the plant, as if you were checking its growth stage.

Later the rice may appear stunted. When the flag leaves emerge, they may be three to 10 times shorter than normal and twisted or otherwise deformed. This is followed by the emergence of malformed seedheads and hooked or “beaked” individual rice seeds.

Glyphosate drift to rice after the PI growth stage is devastating on rice yield. Newpath drift after PI is less devastating on yields, but can cause stunting and malformed leaves and seedheads, depending on the rate of drift.

Arkansas has some of the best aerial applicators in the world. I believe that through awareness of the problem we can manage glyphosate drift ourselves and avoid regulations that would limit the usefulness of glyphosate and the Roundup Ready technologies.

About half of the drift complaints I am involved in occur from ground rigs. Using a ground rig with all the latest drift reduction technology does not mean that chemicals will not move under any conditions. Good judgment about just how hard the wind is blowing is your best defense against injuring your or your neighbors' crops.

Bob Scott is the University of Arkansas Extension weed specialist. e-mail:[email protected]